Power control circuit for sterilized devices, and associated systems and methods

ABSTRACT

A power control circuit for use with devices that will be placed in a flammable sterilizing gas includes a bi-stable switch that is configured to produce an output to place the circuitry of a connected device in a run state or a sleep state. The bi-stable switch controls one or more transistors to drain energy from energy storage devices in the circuitry of the connected device to a level below an ignition level of a sterilizing gas. A remotely actuatable switch can be actuated from outside of a packaging in which the power control circuit is placed to cause the bi-stable switch to produce an output that puts the circuitry in the run state without removing the power control circuit from the packaging.

The present application is a divisional of U.S. patent application Ser.No. 16/264,315, filed on Jan. 31, 2019, which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The presently disclosed technology relates generally to electronicmedical devices that are to be sterilized in flammable environmentsprior to use and, in particular, to sterilizable trial stimulators foruse with implantable neurological stimulation systems.

BACKGROUND

Neurological stimulators have been developed to treat a variety ofconditions such as pain, movement disorders, functional disorders,spasticity, cardiac disorders, and various other medical conditions.Implantable neurological stimulation systems generally have animplantable signal generator and one or more leads that deliverelectrical pulses to neurological and/or muscle tissue. Often suchdevices have one or more electrodes that are inserted into the body nearthe target tissue to deliver the electrical pulses for therapeuticeffect.

Once implanted, the signal generator is programmed to supply electricalpulses to the electrodes, which in turn modify the function of thepatient's nervous system, such as by altering the patient'sresponsiveness to sensory stimuli and/or altering the patient'smotor-circuit output. In spinal cord stimulation (SCS) therapy for thetreatment of pain, the signal generator applies electrical pulses to thespinal cord via the electrodes that mask or otherwise alter thepatient's sensation of pain.

In most cases, tests are performed to see if the patient notices animprovement from the application of the therapy pulses before a signalgenerator is implanted into the patient. Accordingly, an external trialstimulator is attached to the implanted electrodes and can be programmedto deliver electrical pulses with varying signal levels, frequencies,time durations etc. If the patient responds well after wearing the trialstimulator, the patient receives a more permanent implantablestimulator. The implantable stimulator can be programmed with thetherapy regimen that was determined to be the most beneficial during thetrial period. If necessary, the signal generator can be furtherprogrammed while implanted to fine tune the most beneficial therapyregimen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic illustration of an implantable spinalcord modulation system positioned at a patient's spine to delivertherapeutic signals in accordance with some embodiments of the presenttechnology.

FIG. 2 illustrates a trial stimulator that is placed in a sterilepackage and that wirelessly communicates with a programming unit inaccordance with some embodiments of the disclosed technology.

FIG. 3 is a block diagram of a power control circuit for selectivelyreducing stored energy in a trial stimulator to be sterilized inaccordance with some embodiments of the disclosed technology.

FIG. 4 is a schematic diagram of a power control circuit for selectivelyreducing stored energy in a trial stimulator to be sterilized inaccordance with some embodiments of the disclosed technology.

DETAILED DESCRIPTION

The present technology is directed generally to power control circuitsfor selectively powering circuit components and, in some embodiments forselectively powering circuit components in sterilizable devices, andassociated systems and methods. In some embodiments, the presentlydisclosed technologies are directed to systems and devices fordischarging energy storage elements in a medical device that is to beplaced in a flammable sterilizing gas after manufacture and prior touse. For example, a bi-stable switch can control one or more transistorsto drain energy from an energy storage device to a level below anignition level of a sterilizing gas. The bi-stable switch can betriggered to change states via a remotely actuatable switch from outsidea sealed packaging in which the circuit is placed so as not to break thesealed package in the process of re-activating the medical device.

Definitions

Unless otherwise stated, the terms “about” and “approximately” refer tovalues within 10% of a stated value.

As used herein, the term “and/or,” as in “A and/or B” refers to A alone,B alone and both A and B.

References to “some embodiments,” “one embodiment,” or the like, meanthat the particular feature, function, structure or characteristic beingdescribed is included in at least one embodiment of the disclosedtechnology. Occurrences of such phrases in this specification do notnecessarily all refer to the same embodiment. On the other hand, theembodiments referred to are not necessarily mutually exclusive. Elementsdescribed in the context of representative devices, systems and methodsmay be applied to other representative devices, systems and methods in avariety of suitable manners.

To the extent any materials incorporated herein by reference conflictwith the present disclosure, the present disclosure controls.

As used herein, and unless otherwise noted, the terms “modulate,”“modulation,” “stimulate,” and “stimulation” refer generally to signalsthat have an inhibitory, excitatory, and/or other effect on a targetneural population. Accordingly, a spinal cord “stimulator” can have aninhibitory effect on certain neural populations.

System Overview

FIG. 1 schematically illustrates a representative patient therapy system100 for treating a patient's neurological disorders, arranged relativeto the general anatomy of the patient's spinal column 191. The system100 can include a signal generator 101 (e.g., an implanted orimplantable pulse generator or IPG), which may be implantedsubcutaneously within a patient 190 and coupled to one or more signaldelivery elements or devices 110. The signal delivery elements ordevices 110 may be implanted within the patient 190, at or off thepatient's spinal cord midline 189. The signal delivery elements 110carry features for delivering therapy to the patient 190 afterimplantation. The signal generator 101 can be connected directly to thesignal delivery devices 110, or it can be coupled to the signal deliverydevices 110 via a signal link, e.g., a lead extension 102. In someembodiments, the signal delivery devices 110 can include one or moreelongated lead(s) or lead body or bodies 111 (identified individually asa first lead 111 a and a second lead 111 b). As used herein, the termssignal delivery device, signal delivery element, lead, and/or lead bodyinclude any of a number of suitable substrates and/or supporting membersthat carry electrodes/devices for providing therapy signals to thepatient 190. For example, the lead or leads 111 can include one or moreelectrodes or electrical contacts that direct electrical signals intothe patient's tissue, e.g., to provide for therapeutic relief. In someembodiments, the signal delivery elements 110 can include structuresother than a lead body (e.g., a paddle) that also direct electricalsignals and/or other types of signals to the patient 190, e.g., asdisclosed in U.S. Patent Application Publication No. 2018/0256892, whichis herein incorporated by reference in its entirety. For example,paddles may be more suitable for patients with spinal cord injuries thatresult in scarring or other tissue damage that impedes signal deliveryfrom cylindrical leads.

In some embodiments, one signal delivery device may be implanted on oneside of the spinal cord midline 189, and a second signal delivery devicemay be implanted on the other side of the spinal cord midline 189. Forexample, the first and second leads 111 a, 111 b shown in FIG. 1 may bepositioned just off the spinal cord midline 189 (e.g., about 1 mmoffset) in opposing lateral directions so that the two leads 111 a, 111b are spaced apart from each other by about 2 mm. In some embodiments,the leads 111 may be implanted at a vertebral level ranging from, forexample, about T4 to about T12. In some embodiments, one or more signaldelivery devices can be implanted at other vertebral levels, e.g., asdisclosed in U.S. Pat. No. 9,327,121, which is herein incorporated byreference in its entirety.

The signal generator 101 can provide signals (e.g., electrical signals)to the signal delivery elements 110 that excite and/or suppress targetnerves. The signal generator 101 can include a machine-readable (e.g.,computer-readable) or controller-readable medium (e.g. a memory circuit)containing instructions that are executable by a processor forgenerating suitable therapy signals. The signal generator 101 and/orother elements of the system 100 can include one or more processor(s)107, memory unit(s) 108, and/or input/output device(s) 112. Accordingly,instructions for performing tasks such as providing modulation signals,setting battery charging and/or discharging parameters, and/or executingother associated functions can be stored on or in computer-readablemedia located at the signal generator 101 and/or other systemcomponents. Further, the signal generator 101 and/or other systemcomponents may include dedicated hardware for executingcomputer-executable instructions or configured logic circuitry such asFPGAs to perform any one or more methods, processes, and/orsub-processes described in the materials incorporated herein byreference. The dedicated hardware also serve as “means for” performingthe methods, processes, and/or sub-processes described herein. Thesignal generator 101 can also include multiple portions, elements,and/or subsystems (e.g., for directing signals in accordance withmultiple signal delivery parameters), carried in a single housing, asshown in FIG. 1 , or in multiple housings.

The signal generator 101 can also receive and respond to an input signalreceived from one or more sources. The input signals can direct orinfluence the manner in which the therapy, charging, and/or processinstructions are selected, executed, updated, and/or otherwiseperformed. The input signals can be received from one or more sensors(e.g., an input device 112 shown schematically in FIG. 1 for purposes ofillustration) that are carried by the signal generator 101 and/ordistributed outside the signal generator 101 (e.g., at other patientlocations) while still communicating with the signal generator 101. Thesensors and/or other input devices 112 can provide inputs that depend onor reflect a patient state (e.g., patient position, patient posture,and/or patient activity level), and/or inputs that arepatient-independent (e.g., time). Still further details are included inU.S. Pat. No. 8,355,797, which is herein incorporated herein byreference in its entirety.

In some embodiments, the signal generator 101 and/or signal deliverydevices 110 can obtain power to generate the therapy signals from anexternal power source 103. For example, the external power source 103can by-pass an implanted signal generator and be used to generate atherapy signal directly at the signal delivery devices 110 (or viasignal relay components). In some embodiments, the external power source103 can transmit power to the implanted signal generator 101 and/ordirectly to the signal delivery devices 110 using electromagneticinduction (e.g., RF signals). For example, the external power source 103can include an external coil 104 that communicates with a correspondinginternal coil (not shown) within the implantable signal generator 101,signal delivery devices 110, and/or a power relay component (not shown).The external power source 103 can be portable for ease of use.

In some embodiments, the signal generator 101 can obtain the power togenerate therapy signals from an internal power source, in addition toor in lieu of the external power source 103. For example, the implantedsignal generator 101 can include a non-rechargeable battery or arechargeable battery to provide such power. When the internal powersource includes a rechargeable battery, the external power source 103can be used to recharge the battery. The external power source 103 canin turn be recharged from a suitable power source (e.g., conventionalwall power).

During at least some procedures, an external stimulator or trialstimulator 105 can be coupled to the signal delivery elements 110 duringan initial procedure, prior to implanting the signal generator 101. Forexample, a practitioner (e.g., a physician and/or a companyrepresentative) can use the trial stimulator 105 to vary the modulationparameters provided to the signal delivery elements 110 in real time andselect optimal or particularly efficacious parameters. These parameterscan include the location from which the electrical signals are emitted,as well as the characteristics of the electrical signals provided to thesignal delivery devices 110. In some embodiments, input is collected viathe external stimulator or trial stimulator and can be used by theclinician to help determine what parameters to vary.

In a typical process, the practitioner uses a cable assembly 120 totemporarily connect the trial stimulator 105 to the signal deliverydevice 110. The practitioner can test the efficacy of the signaldelivery devices 110 in an initial position. The practitioner can thendisconnect the cable assembly 120 (e.g., at a connector 122), repositionthe signal delivery devices 110, and reapply the electrical signals.This process can be performed iteratively until the practitionerdetermines the desired position for the signal delivery devices 110.Optionally, the practitioner may move the partially implanted signaldelivery devices 110 without disconnecting the cable assembly 120.Furthermore, in some embodiments, the iterative process of repositioningthe signal delivery devices 110 and/or varying the therapy parametersmay not be performed.

The signal generator 101, the lead extension 102, the trial stimulator105 and/or the connector 122 can each include a receiving element 109 orcoupler that is configured to facilitate the coupling and decouplingprocedure between the signal delivery devices 110, the lead extension102, the pulse generator 101, the trial stimulator 105 and/or theconnector 122. The receiving elements 109 can be at least generallysimilar in structure and function to those described in U.S. PatentApplication Publication No. 2011/0071593, which is herein incorporatedby reference in its entirety.

After the signal delivery elements 110 are implanted, the patient 190can receive therapy via signals generated by the trial stimulator 105,generally for a limited period of time. During this time, the patientwears the cable assembly 120 and the trial stimulator 105 is securedoutside the body. Assuming the trial therapy is effective or shows thepromise of being effective, the practitioner then replaces the trialstimulator 105 with an implantable signal generator 101, and programsthe signal generator 101 with therapy programs that are selected basedon the experience gained during the trial period. Optionally, thepractitioner can also replace the signal delivery elements 110. Once theimplantable signal generator 101 has been positioned within the patient190, the therapy programs provided by the signal generator 101 can stillbe updated remotely via a wireless physician's programmer 117 (e.g., aphysician's laptop, a physician's remote or remote device, etc.) and/ora wireless patient programmer 106 (e.g., a patient's laptop, patient'sremote or remote device, etc.). Generally, the patient 190 has controlover fewer parameters than does the practitioner. For example, thecapability of the patient programmer 106 may be limited to startingand/or stopping the signal generator 101, and/or adjusting the signalamplitude. The patient programmer 106 may be configured to accept inputscorresponding to pain relief, motor functioning and/or other variables,such as medication use. Accordingly, more generally, the presenttechnology includes receiving patient feedback that is indicative of, orotherwise corresponds to, the patient's response to the signal. Feedbackincludes, but is not limited to, motor, sensory, and verbal feedback. Inresponse to the patient feedback, one or more signal parameters can beadjusted, such as frequency, pulse width, amplitude or deliverylocation.

Sterilization

Because the trial stimulator 105 is connected to the signal deliverydevices 110 within a sterile environment, the trial stimulator 105 mustitself be sterile prior to use. As shown in FIG. 2 , the trialstimulator is preferably stored in a sterile package 150 that is openedjust prior to connecting the trial stimulator to the patient. In someembodiments, the sterile package 150 is a pouch that is permeable tosterilizing gasses but impermeable to microbe contaminants (e.g.bacteria, viruses, molds etc.). Suitable pouches are made from Tyvek® orother similar gas-permeable materials.

The most common type of gas used to sterilize medical devices isethylene oxide (ETO). While this gas is effective for sterilizingequipment, it is also highly flammable. Ethylene oxide can ignite whenexposed to an electrical energy discharge as low as 60 micro-joules.Care must be taken to ensure that any electrical circuitry placed in thepackaging is completely or nearly completely discharged prior toexposure to the flammable sterilizing gas.

In addition, it is also beneficial if the trial stimulator 105 can betested prior to its removal from the sterile packaging. Such testing canconfirm the functionality of the unit prior to be being brought into asterile operating theatre. In addition to or in lieu of testing, it mayalso be desirable to update the trial stimulator firmware and/or othersoftware prior to removing the trial stimulator 105 from the packaging.

Given these implementation targets, an aspect of the presently disclosedtechnology includes a power control circuit that can be used with atrial stimulator to reduce the amount of energy stored in the trialstimulator to a level that allows the trial stimulator to be safelyexposed to (e.g. placed in) a flammable sterilizing gas. In addition,the presently disclosed power control circuit can limit the batterydrain of the trial stimulator while the trial stimulator is in a “sleepstate” so that the battery remains sufficiently charged to power thecircuit. In yet another aspect, the power control circuit can activateor awaken the trial stimulator while it is still in the sterilepackaging. These and other aspects of the disclosed technology arediscussed in further detail below. Although the power control circuit ofthe disclosed technology is described with respect to its use with atrial stimulator for nerve stimulation, it will be appreciated that thepower control circuit can be used with other electronic devices that areto be stored prior to use and, in particular, with other electronicdevices that are to be sterilized in a flammable gas environment.

FIG. 2 shows an environment in which a trial stimulator 105 is stored ina sterile packaging 150. Upon manufacture, the trial stimulator 105 isprogrammed with firmware required to control the internal circuitry usedto deliver stimulation pulses to one or more electrodes in a patient.Once it is confirmed that the trial stimulator 105 is fully functional,it is placed in the packaging 150 and subjected to a sterilizingprocedure. In some embodiments, the packaging 150 is a gas-permeablepouch (e.g. formed from Tyvek® or another suitable material) that allowsa gas such as ethylene oxide to penetrate into the packaging andsterilize the trial stimulator 105 inside. The gas is withdrawn throughthe permeable material and the contents of the packaging 150 remainssterile as long as the packaging remains sealed.

Prior to use with a patient, the trial stimulator 105 in the sterilepackaging 150 is awakened and begins to communicate with an externaldevice such as a pulse programmer 160. Suitable modes of communicationinclude short distance wireless communication protocols (e.g. Bluetooth,ZigBee, 802.11, infrared and/or other suitable protocols). In someembodiments, the trial stimulator 105 is awakened from a sleep statewhile still sealed in the sterile packaging 150. The trial stimulator150 begins wirelessly communicating with the programmer 160 to confirmthat the trial stimulator 105 is working and/or to confirm that abattery within the trial stimulator has sufficient power to operate thetrial stimulator, and/or to update firmware and/or other storedparameters if necessary. Because the sterilizing gas has been removedfrom the packaging 150 prior to awakening the trial stimulator, there isno longer a risk of explosion if the trial stimulator is powered up. Insome embodiments, the power control circuit draws minimal power from thebattery so that the power control circuit is able to keep the trialstimulator in a sleep state for several years without draining thebattery to the point that it cannot power the trial stimulator.

FIG. 3 is a block diagram of a power control circuit 200 configured inaccordance with some embodiments of the disclosed technology. The powercontrol circuit 200 incudes a power source such as a battery 202 orother energy storage device (e.g. an energy storage capacitor). Thebattery voltage (Vbat) is connected to the trial stimulator circuitry206 via an electronically controlled switch (e.g. a transistor) 204. Thecircuitry 206 includes, among other things, a processor, non-volatilememory for storing instructions or parameters, a radio transceiver forcommunicating with an external device and/or voltage regulators thatproduce higher voltages used to deliver the therapeutic pulses to thepatient. In addition, the circuitry 206 may include energy storagedevices (e.g. capacitors) that store energy in the trial stimulator.

In order to avoid storing enough energy in the trial stimulator toignite a sterilizing gas, a bi-stable switch 220 controls one or moretransistors 204, 222 to put the circuitry of the trial stimulator in asleep state. In some embodiments, the bi-stable switch 220 puts thetrial stimulator in a sleep state by turning off the transistor 204 sothat power from the battery does not reach the circuitry 206 in thetrial stimulator. In addition, any bus voltage levels and stored energyon the energy storage devices that could potentially ignite asterilizing gas are drawn down to zero or near zero potential throughone or more transistors 222.

In some embodiments, the bi-stable switch 220 operates as a flip flopcircuit to produce an output that places the trial stimulator in a runstate when battery power is first applied to the switch 220. A processor(not shown) within the trial stimulator circuitry 206 can provide asignal on a line 208 that causes the bi-stable switch 220 to changestates and produce a signal that puts the trial stimulator in a sleepstate. The signal on line 208 from the processor can be activated once aself-test routine is complete. Alternatively, the processor or otherlogic circuit can receive a command from an external programmer (notshown) via a wireless connection to put the trial stimulator in a sleepstate.

A remotely actuatable switch 226 (e.g. a switch that is actuatable fromoutside the packaging 150 shown in FIG. 2 ) is provided to change thestate of the bi-stable switch 220 and cause the bi-stable switch toproduce a signal causing the connected circuitry to exit the sleep stateand enter the run state. The switch 226 can be operated through thesterile packaging so that the trial stimulator need not be removed fromthe packaging in order to cause the trial stimulator to enter the runstate. Suitable remotely actuatable switches include, but are notlimited to, magnetically activated reed switches, mechanical switches,pressure activated switches, light activated switches, shock activatedswitches, and/or Hall-effect switches. In some embodiments, the switch226 is mechanically operated so that it does not need to be poweredwhile the trial stimulator is in the sleep state.

In some embodiments, the switch 226 is a magnetically activated reedswitch. Placing a magnet on the outside of the sterile packaging nearthe switch 226 closes the reed switch and causes the power controlcircuit to produce an output that puts the trial stimulator in the runstate. More particularly, closing the switch 226 causes the bi-stableswitch 200 to generate an output that turns on the transistor 204 andapplies the battery voltage to the circuitry 206 within the trialstimulator. In addition, closing the switch 226 turns off the transistor222 and allows the energy storage devices in the trial stimulator tocharge.

FIG. 4 is a schematic diagram of a representative embodiment of thepower control circuit 200 shown in FIG. 3 . The power control circuit200 includes the bi-stable switch 220 that is configured as a JK flipflop. The flip flop includes two cross-connected FET transistors 250 and254. Each of the first and second transistors 250, 254 has a sourceterminal that is grounded. The drain terminal of the first transistor250 is connected through a first 10 MΩ resistor 258 to the batteryvoltage Vbat. Similarly, the drain of the second transistor 254 isconnected through a second 10 MΩ resistor 260 to the battery voltageVbat. The node between the drain terminal of the second transistor 254and the second resistor 260 is connected through a first 1 MΩ resistorto the gate of the first transistor 250. Similarly, the node between thedrain of the first transistor 250 and first resistor 258 is connectedthrough a second 1 MΩ resistor to the gate of the second transistor 254.In this way, when the first transistor 250 is turned on, the secondtransistor 254 is held off. Conversely, when the second transistor 254is turned on, the first transistor 250 is held off.

In the embodiment shown in FIG. 4 , an output 262 of the flip flopcircuit that is taken at the node between the drain of the secondtransistor 254 and the second resistor 260 drives a number oftransistors that reduce the energy stored in a connected circuit whenthe circuit is in a sleep state. As shown, the output 262 feeds a gateof a p-type FET transistor 270 such that when the output 262 is a logiclow level, the transistor 270 is turned on and connects the batterypower to the connected circuitry 206. In addition, the output 262 isconnected to gates of one or more n-type FET transistors 280 a, 280 betc. When the output 262 is a logic low level, transistors 280 a, 280 bare turned off.

When the flip flop changes states, the output 262 goes to a logic highlevel and the transistor 270 is turned off, thereby disconnecting thebattery power from the connected circuitry 206. In addition, the logichigh level on output 262 turns the transistors 280 a, 280 b on. Thetransistors 280 a, 280 b are configured to connect any busses and anyenergy storage devices on the busses or other powered lines to groundthrough a 1 KΩ resistor so that their voltage is zero or near zero andthe energy stored on the capacitors is less than an ignition energylevel of a flammable sterilization gas. In some embodiments, the energystored in the connected circuitry 206 while in the sleep state isreduced to less than 1/10th of that which could ignite a sterilizing gas(e.g. reduced to about 6 uJoules or less for ETO).

With the first transistor 250 conducting and the second transistor 254in the non-conducting state, the connected circuitry 206 is put into asleep state. The first and second transistors 250, 254 have a very lowleakage current and the 10 MΩ resistors in series with the drainelectrodes limits the current of the conducting transistor in the sleepstate to a low level (3.6V/10MΩ=360 nA) such that the battery drain isminimal during the sleep state.

In some embodiments, a first 1000 pF capacitor 264 is connected betweenthe battery voltage and the gate of the second transistor 254.Similarly, a second 1000 pF capacitor 266 is connected to the gate ofthe first transistor 250 and ground. When battery power is first appliedto the power control circuit, the first capacitor 264 acts as a shortand the battery voltage appears at the gate of the second transistor 254turning it on and producing a logic low level on the output 262 therebyplacing the connected circuitry 206 in a run state. In this way, if anew battery is placed into the circuit, the connected circuitry 206 willimmediately begin to operate in the run state. Capacitors 264, 266 alsoshunt stray EMF signals to ground or the battery and lessen thelikelihood that any such EMF will change the state of the flip flop.

The power control circuit 200 will keep the connected circuitryoperating in the run state until it is commanded to turn off. In someembodiments, an N-type FET transistor 290 has a drain connected to thegate of the second transistor 254. When the transistor 290 is turned on,the gate of the second transistor 254 is connected to ground and thesecond transistor 254 is turned off. The output 262 of the power controlcircuit then goes to a logic high level and the connected circuitryenters the sleep state. In some embodiments, a signal that controls thetransistor 290 is received from a processor or other logic circuit inthe connected circuitry 206, such that when the circuit completes aself-test or is commanded by an external controller, the processor putsa logic level on the gate of the transistor 290 to take the circuitryout of the run state and put it into the sleep state. Aresistor/capacitor combination are connected to the gate of transistor290 to de-bounce any jitters on the signal applied to the gate oftransistor 290.

The power control circuit 200 will continue to produce an output to keepthe connected circuitry in the sleep state until the flip flop changesstates. In some embodiments, a remotely actuatable switch 300 such as amagnetically activated reed relay is connected between the batteryvoltage through a 10 KΩ resistor 292 and diode 294 to the gate of thesecond transistor 254. When the remotely actuatable switch 300 isclosed, the battery voltage is applied to the gate of the transistor 254thereby driving the output 262 to a logic low level and putting theconnected circuitry 206 back in the run state. In some embodiments, aresistor divider is connected between the resistor 292 and the in-linediode 294 so that a processor or other logic circuit can detect whetherthe switch 300 is closed or open depending on the voltage level producedby the resistor divider.

The remotely actuatable switch 300 can be activated from outside of thesterile packaging so that the connected circuitry can be turned onwithout removing it from the packaging. As indicated above, other typesof switches that can be activated through the sterile packaging couldalso be used such as pressure switches, shock activated switches, lightactivated switches or even mechanically controlled switches that can beactivated through the packaging. A Hall effect switch can also be used,depending on the current draw required to remain powered.

As will be appreciated, the power control circuit 200 operates toselectively apply the battery voltage to connected circuitry in a runstate and to bleed or drain energy from energy storage devices in asleep state. In some embodiments, the power control circuit may leavethe battery voltage connected to some circuitry, provided that thecurrent drain is not too great for long periods of storage (e.g. severalmonths to years). However, the power control circuit 200 should drainthe energy from the busses/capacitors such that the total energy storedin the circuitry is less than a level that could ignite any sterilizinggas.

From the foregoing, it will be appreciated that specific embodiments ofthe disclosed technology have been described herein for purposes ofillustration, but that various modifications may be made withoutdeviating from the technology. For example, bi-stable switchconfigurations other than a JK flip flop could be used including D-typeflip flops, RS-type flip flops or other logic configurations that areconfigured to retain a state until directed to change states and thatdraw little power. In general, any bi-stable switch configuration withthe following features could be used: 1) the bi-stable switch state ismaintained with a very small amount of power such that the battery isnot unduly depleted in long-term storage; 2) the bi-stable switchreliably powers up in a known state, either on or off, when the batteryis replaced; 3) the bi-stable switch is tolerant of EMF interferencesuch that it cannot easily be switched by such fields. Any of theseswitch features might be relaxed in embodiments that do not requirethem. In addition, the disclosed embodiments can be used with circuitryother than implantable circuitry for treating pain with electricalpulses. For example, the disclosed embodiments can be used withimplantable cardiac pacemakers or defibrillators or other implantable ornon-implantable electronic devices that require sterilization before useand that store sufficient energy that could ignite a flammablesterilizing gas. Other uses for the disclosed technology include use intreating acute or episodic conditions with neuro-stimulators. Thesedevices require leads that pierce the skin and are generally implantedunder sterile conditions. A sterile stimulator with the disclosed powercontrol circuit can make installation and testing of these leads moreconvenient for the patient and physician.

In some embodiments, the disclosed technology can be used with devicesthat are to be placed in a sleep state and de-powered to a safe handlinglevel without the need to be placed in an explosive sterilizingenvironment. For example, circuitry for high voltage power supplies suchas the type used in X-ray imaging equipment, ultrasound imaging, MRIdevices, cathode ray displays or other vacuum tube-based designs orother devices that produce voltage levels that are potentially dangerousif touched or if they arc. Other representative non-medical devices thatcan be powered down in a sleep state include circuits for use in rocketsor other devices that are sometimes exposed to flammable environmentsduring use or storage. The disclosed circuitry can be used to place suchdevices in a sleep state until they are to be awakened in an environmentwhere the presence of higher voltages is not dangerous.

Certain aspects of the technology described in the context of particularembodiments may be combined or eliminated in other embodiments. Forexample, the embodiments described above can be produced without abattery and the battery supplied by an end user prior to sterilizationand storage. Further, while advantages associated with certainembodiments of the disclosed technology have been described in thecontext of those embodiments, other embodiments may also exhibit suchadvantages, and not all embodiments need necessarily exhibit suchadvantages to fall within the scope of the present technology.Accordingly, the disclosure and associated technology can encompassother embodiments not expressly shown or described herein.

I claim:
 1. A power control circuit configured to selectively place adevice into a run state or a sleep state, the power control circuitcomprising: a flip flop circuit that is configured to produce an outputthat places a connected device in a run state or a sleep state; atransistor that is controlled by the output of the flip flop circuit todrain stored energy from one or more energy storage devices of theconnected device when the connected device is in the sleep state; and aremotely actuatable switch that is configured to cause the flip flopcircuit to produce the output that puts the connected device in the runstate without physically touching the switch.
 2. The power controlcircuit of claim 1, wherein the transistor is a first transistor, thepower control circuit further comprising a second transistor that iscontrolled by the output of the flip flop circuit to apply power to theconnected device from an energy source while in the run state.
 3. Thepower control circuit of claim 2, further comprising a capacitorconnected between the power source and the second transistor such that,upon application of power from the power source to the flip flopcircuit, the power turns on the second transistor and produces theoutput that causes the connected device to operate in the run state. 4.The power control circuit of claim 1, wherein the flip flop circuitcomprises a pair of cross-connected transistors, and wherein each of thecross-connected transistors is connected in series with a resistance. 5.The power control circuit of claim 1, wherein the remotely actuatableswitch is a magnetically actuated switch.
 6. The power control circuitof claim 1, wherein the remotely actuatable switch is a magneticallyactivated reed switch.
 7. The power control circuit of claim 1, whereinthe remotely actuatable switch is controllable by light.
 8. The powercontrol circuit of claim 1, wherein the remotely actuatable switch iscontrollable with a shock.
 9. The power control circuit of claim 1,wherein the remotely actuatable switch is pressure activated.
 10. Apower control circuit configured to selectively place a device into arun state or a sleep state, the power control circuit comprising: aswitch configured to produce an output that places a connected device ina run state or a sleep state; a first transistor controlled by theoutput of the switch and configured to drain stored energy from theconnected device when the connected device is in the sleep state; and asecond transistor controlled by the output of the switch andelectrically coupled to the connected device and an energy source, thesecond transistor being configured to inhibit current flow from theenergy source to the connected device when the connected device is inthe sleep state.
 11. The power control circuit of claim 10, wherein theswitch is a bi-stable switch, the power control circuit furthercomprising a remotely actuatable switch that, when actuated, causes thebi-stable switch to produce the output that puts the connected device inthe run state.
 12. The power control circuit of claim 10, wherein theswitch is a flip flop circuit, and wherein, upon receiving power, theflip flop circuit produces the output that causes circuitry of theconnected device to operate in the run state.
 13. The power controlcircuit of claim 10, wherein the switch is a flip flop circuitcomprising a pair of cross-connected transistors, and wherein each ofthe cross-connected transistors is connected in series with aresistance.
 14. A method for controlling power to a device havingcircuitry configured to be placed in a flammable environment before use,the method comprising: in a power control circuit including a powersource, a switch connected to the power source, and a transistorelectrically coupled to the power source and circuitry of the device,the transistor being in a first state during which current flow betweenthe power source and the circuitry is inhibited: receiving a signal atthe switch; and in response to the received signal, producing an outputfrom the switch to cause the transistor to transition to a second stateand thereby connect the power source to the circuitry.
 15. The method ofclaim 14, wherein the transistor is a first transistor and the powercontrol circuit further comprises a second transistor connected to thedevice, wherein the output from the switch causes the second transistorto open and thereby prevent energy from the device from being drained.16. The method of claim 14, wherein the transistor is a first transistorand the power control circuit further comprises a second transistorconnected to the device and configured to prevent the device fromstoring energy when the device is in the sleep state.
 17. The method ofclaim 14, wherein the output is a first output, the method furthercomprising producing a second output from the switch to cause thetransistor to transition to the first state and disconnect the powersource from the circuitry.
 18. The method of claim 14, furthercomprising actuating a remotely actuatable switch positioned between thepower source and the switch, causing the signal to be generated.
 19. Themethod of claim 14, further comprising magnetically or opticallyactuating a remotely actuatable switch, causing the signal to begenerated.
 20. The method of claim 14, wherein the switch is a flip flopcircuit comprising a pair of cross-connected transistors each connectedin series with a resistance.